1. Field of the Invention
The present invention relates to a method and apparatus for storing a polished semiconductor wafer after its CMP (i.e., chemical mechanical polishing) process, and more particularly to the method and apparatus for temporarily storing the polished semiconductor wafer in a water tank after its CMP process and before its post-CMP cleaning process, in which the post-CMP cleaning process abrasives (i.e., abrasive grains or powder) for example such as those of alumina, silica, oxidizing agents, or of like substances) used in the CMP process and the wafer""s debris remaining on the surface of the polished semiconductor wafer are removed.
2. Description of the Related Art
In a conventional process for forming a metallic wiring in a surface of a semiconductor wafer through a so-called xe2x80x9cdamascene processxe2x80x9d: first, an insulation film is formed on a surface of a semiconductor substrate which is constructed of the semiconductor wafer; secondly, a wiring trench and/or a connecting hole connected with a lower wiring layer is formed in the insulation film; and, lastly, the metallic wiring and/or a connecting plug is formed by forming a metallic wiring film of copper or like metal on the semiconductor substrate through an electroplating process of copper or like metal and then removing excess metal or excess copper from the metallic wiring film through a CMP operation to form metallic wiring and/or a connecting plug on the semiconductor substrate.
After completion of the CMP operation, any abrasive and any debris of the thus polished semiconductor wafer are removed from the surface of the polished semiconductor wafer through a post-CMP cleaning operation which follows the CMP operation. In general, at this time, there is a predetermined period of wafer""s waiting time between the CMP operation and such post-CMP cleaning operation of the polished semiconductor wafer. In case that the surface of the polished semiconductor wafer becomes dry in the above-mentioned wafer""s waiting time, it becomes very hard to remove both the abrasive and the debris of the polished semiconductor wafer from such dried surface. Consequently, in order to keep the surface of the polished semiconductor wafer wet after polishing, the polished-semiconductor wafer having been subjected to the CMP operation is immersed in pure water of a water tank during the above-mentioned wafer""s waiting time, as disclosed in Japanese Patent Laid-Open No. Hei 10-214802.
FIG. 9 is a flowchart of process steps performed after completion of the CMP operation of the Cu (i.e., copper) wiring of the semiconductor wafer when a Cu damascene wiring is formed according to a conventional method, illustrating both a conventional CMP unit for CMP polishing the copper, wiring and a conventional post-CMP cleaning unit.
In general, a plurality of (i.e., approximately ten to thirty semiconductor wafers are housed in a wafer carrier to form a batch-processed work called a xe2x80x9clotxe2x80x9d) which is transferred between adjacent carriers of a plurality of processing units.
In a process step S1 of the flowchart shown in FIG. 9, the polished semiconductor wafer has a Cu film formed on its surface in a Cu film formation unit. Then, the process step S1 is followed by a subsequent process step S2. As a result, the xe2x80x9clotxe2x80x9d is transferred from the above Cu film formation unit to a loader chamber 11 of a copper chemical mechanical polishing (i.e., Cu-CMP) unit 10.
More specifically, in the process step S2 for performing the Cu-CMP operation, a set of the polished semiconductor wafers of approximately one to four pieces is retrieved from the wafer carrier having been mounted in the loader chamber 11, is set in a polishing chamber 13 of the Cu-CMP unit 10 and subjected to the CMP process. Since the polished semiconductor wafer has a diameter of approximately 30 cm, it is not practical to prepare a CMP unit which is capable of treating the above-mentioned xe2x80x9clotxe2x80x9d of large-diameter semiconductor wafers at a time because of an enormous size of such CMP unit, wherein the xe2x80x9clotxe2x80x9d is composed of a plurality of such large-diameter semiconductor wafers.
Consequently, in the process step S2 shown in the flowchart of FIG. 9, in general, approximately one to four semiconductor wafers are treated at a time. After completion of the CMP operation, these polished semiconductor wafers are housed in another wafer carrier provided in an unloader chamber 12 of the CMP unit 10, and enter a waiting mode in this unloader chamber 12 and kept therein until another wafer carrier is filled with these polished semiconductor wafers having been subjected to the CMP operations. On the other hand, this unloader chamber 12 is provided with a wafer storing water tank (not shown), in which the thus polished semiconductor wafers are stored in water, and thereby preventing their surfaces from becoming dry after completion of their CMP polishing operations.
After completion of the process step S2 for performing the Cu-CMP operations of copper or metallic wirings of the polished semiconductor wafers of the above-mentioned xe2x80x9clotxe2x80x9d, another wafer carrier is transferred from the unloader chamber 12 to a loader chamber 16 of a post-CMP cleaning unit 14 to enter a process step S3 subsequent to the process step S2. In the process step S3, the xe2x80x9clotxe2x80x9d is subjected to the post-CMP cleaning process. On the other hand, the loader chamber 16 of the post-CMP cleaning unit 14 is also provided with another wafer storing water tank for receiving the polished semiconductor wafers having been subjected to the CMP operations, wherein these polished semiconductor wafers are stored in water of another water tank to prevent their surfaces from drying.
In the post-CMP cleaning unit 14 shown in FIG. 9, a cleaning or post-CMP cleaning chamber 15 is disposed adjacent to the loader chamber 16. Consequently, the polished semiconductor wafers are transferred from the loader chamber 16 to this post-CMP cleaning chamber 15 singly and successively, then subjected to scrubbing operations with the use of both a brush and a cleaning liquid issued to the individual polished semiconductor wafers, and lastly rinsed out with the use of alcohol and water. After that, the polished semiconductor wafers thus rinsed out are dried in a drying chamber 17. This drying chamber 17 is disposed adjacent to the post-CMP cleaning chamber 15, as shown in FIG. 9. The polished semiconductor wafers thus dried up are then transferred to further another wafer carrier 22 which is provided in an unloader chamber 19 disposed adjacent to the drying chamber 17.
After completion of the post-CMP cleaning operation in the process step S3, the process step S3 is followed by its subsequent process step S4. In this subsequent process step S4, for example, a cover film is formed on the surface of each of the polished semiconductor wafers of the further another wafer carrier.
Shown in FIG. 10 is a conventional apparatus for storing the polished semiconductor water in a wafer storing water tank 18 thereof. In this conventional apparatus, the polished semiconductor wafer is immersed in pure water received in the wafer storing water tank 18. More specifically, as shown in FIGS. 9 and 10, the wafer storing water tank 18 shown in FIG. 10 is installed in the unloader chamber 12 (shown in FIG. 9) of the CMP unit 10, and also installed in the loader chamber 16 (shown in FIG. 9) of the post-CMP cleaning unit 14. In operation, the wafer storing water tank 18 is filled with pure water 43, so that the polished semiconductor wafers 20 housed in the wafer carrier 22 are immersed in the pure water 43 of the wafer storing water tank 18, to which tank 18 the pure water is constantly supplied from the outside.
There is another conventional method, in which the polished semiconductor wafers are not immersed in the pure water 43 but sprayed with pure water. Shown in FIG. 11 is a part of a conventional apparatus carrying out the latter conventional method for spraying the polished semiconductor wafers 20 with a spray 24 of pure water having a temperature ranging from more than 25xc2x0 C. to 28xc2x0 C. In the latter conventional method, the polished semiconductor wafers 20 are housed in the wafer carrier 22 and subjected to the spray 24 of pure water.
In the conventional methods and apparatuses described above, the pure water, which is used as the pure water 43 in the wafer storing water tank 18 and also used as the spray 24 in FIG. 11, has a temperature substantially equal to room temperatures ranging from approximately 25 to approximately 28xc2x0 C.
Now, the problems inherent in the conventional methods and apparatuses and therefore solved by the present invention will be described.
For example, in a condition in which the wafer carrier is capable of housing therein twenty-four pieces of the polished semiconductor wafers at a time and the CMP unit 10 is capable of treating four polished semiconductor wafers in approximately 10 to 15 minutes at a time, it takes approximately 60 to 100 minutes to treat the above-mentioned one xe2x80x9clotxe2x80x9d of the polished semiconductor wafers, which requires the polished semiconductor wafers to be temporarily stored in the wafer storing water tank of the unloader chamber 19 in the CMP unit 14 until treatment of this xe2x80x9clotxe2x80x9d of the polished semiconductor wafers is completed. In like manner, in a condition in which the cleaning chamber 15 of the post-CMP cleaning unit 14 is capable of treating each of the polished semiconductor wafers in approximately two or three minutes at a time, it takes approximately 40 to 60 minutes to treat the xe2x80x9clotxe2x80x9d of the polished semiconductor wafers, which requires the polished semiconductor wafers to be temporarily stored in the water tank of the loader chamber 16 in the post-CMP cleaning unit 14 until treatment of this xe2x80x9clotxe2x80x9d of the polished semiconductor wafers is completed. Further, when some trouble occurs in the CMP unit 10 and/or the post-CMP cleaning unit 14, it is necessary to store the polished semiconductor wafers in the water of the water tank or to have these polished semiconductor wafers sprayed with the water for a time period of from approximately several hours to approximately twenty-four hours.
For example, in a polishing operation for forming the Cu (i.e., copper) damascene wiring, when the wafer""s waiting period of time of each of the polished semiconductor wafers between the polishing operation and the post-polishing cleaning operation is large, the Cu or metallic wiring is subjected to corrosion caused by an oxidizing agent. This oxidizing agent is contained in the abrasive used in the polishing operation and remains in the surface of each of the polished semiconductor wafers. As a result of such corrosion of the Cu or metallic wiring of each of the polished semiconductor wafers, the electric resistance of the Cu wiring increases. This is one of problems inherent in the conventional methods and apparatuses.
On the other hand, in a graph of FIG. 12 shows the change in configuration of the Cu or metallic wiring of the polished semiconductor wafer with elapsed period of time due to the corrosion occurring in the metallic wiring. Formed on the surface of the polished semiconductor wafer forming a polished semiconductor substrate 29 shown in FIG. 12 is an insulation film 27 made of SiO2 and the like. A wiring trench and/or a connecting hole are/is formed in a portion of the insulation film 27. A suitable barrier film 25 made of TaN and the like is formed inside the wiring trench and/or the connecting hole. Formed inside the barrier film 25 are a Cu or metallic wiring 23 and/or a connecting hole. Adhered to the surface of the polished semiconductor wafer are the abrasive grain or power and the debris 26 of the polished semiconductor wafer in addition to the oxidizing agent 28 derived from the abrasive grain or powder. The oxidizing agent adhering to the surface of the Cu or metallic wiring 23 chemically attacks the copper or metal forming the Cu or metallic wiring to cause corrosion thereof. Due to such corrosion of the Cu or metallic wiring, the Cu or metallic wiring is reduced in thickness to have its top surface be lower in height than the insulation film 27 surrounding the Cu or metallic wiring on all sides, which forms a shoulder portion in the surface of the polished semiconductor wafer. Due to the presence of such shoulder portion formed in the surface of the polished semiconductor wafer, it is difficult to remove the debris 26 adhering to a corner portion (i.e., shoulder portion) of the wiring trench or of the connecting hole of the polished semiconductor wafer, which impairs the surface of the polished semiconductor wafer in cleaning efficiency. Further, since the thickness of the Cu or metallic wiring of the polished semiconductor wafer is reduced as described above, the electric resistance of the Cu or metallic wiring of the polished semiconductor wafer increases.
The conventional methods, in which each of the polished semiconductor wafer is immersed in pure water of the water tank or sprayed with pure water, pose various types of problems caused by corrosion of the Cu or metallic wiring of the polished semiconductor wafer in addition to the above-mentioned problem.
In view of the above, It is an object of the present invention to provide a method and apparatus for storing a polished semiconductor wafer after its polishing process in which the anticorrosion agent is capable of adhering to the surface of the polished semiconductor wafer to protect its surface against corrosion.
According to a first aspect of the present invention, there is provided a method for storing a polished semiconductor wafer after completion of its CMP process for a period of time intervened between: the CMP process for forming a metallic wiring in the polished semiconductor wafer; and, a cleaning process of the thus polished semiconductor wafer, wherein the cleaning process follows the CMP process, the method including the step of:
keeping the polished semiconductor wafer immersed in pure water, to which water an anticorrosion agent is added, wherein the anticorrosion agent prevents an oxidizing agent contained in an abrasive from chemically attacking the metallic wiring of the polished semiconductor wafer, wherein the abrasive is used in the CMP process.
In the foregoing, a preferable mode is one wherein the pure water is recycled together with the anticorrosion agent through a water tank.
Further, a preferable mode is one wherein the metallic wiring of the polished semiconductor wafer is constructed of a damascene wiring or of a connecting plug.
Still further, a preferable mode is one wherein the metallic wiring of the polished semiconductor wafer is formed of metal selected from the group consisting of: copper; aluminum; alloys of copper; alloys of aluminum; and, copper-aluminum alloys.
Also, a preferable mode is one wherein the anticorrosion agent is made of a compound selected from the group consisting of: benzotriazole; o-tolyltriazole; m-tolyltriazole; p-tolyltriazole; carboxybenzotriazole; l-hydroxybenzotriazole; nitrobenzotriazole; dihydroxypropylbenzotriazole; and, a mixture of at least any two of the above-mentioned compounds.
Further, a preferable mode is one wherein the anticorrosion agent to be added to the pure water is made of benzotriazole.
Still further, a preferable mode is one wherein addition of the anticorrosion agent made of benzotriazole to the pure water is made at a rate of from 0.01% to 5%.
Also, according to a second aspect of the present invention, there is provided a method for storing a polished semiconductor wafer after completion of its CMP process for a period of time intervened between: the CMP process for forming a metallic wiring in the polished semiconductor wafer; and, a cleaning process of the thus polished semiconductor wafer, wherein the cleaning process follows the CMP process, the method including the step of:
keeping the polished semiconductor wafer immersed in pure water having a predetermined temperature, wherein the predetermined temperature is capable of decreasing a rate of chemical reaction occurring in corrosion of the metallic wiring of the polished semiconductor wafer, wherein the corrosion is caused by an oxidizing agent contained in an abrasive, and the abrasive is used in the CMP process.
Also, according to a third aspect of the present invention, there is provided a method for storing a polished semiconductor wafer after completion of its CMP process for a period of time intervened between: the CMP process for forming a metallic wiring in the polished semiconductor wafer; and, a cleaning process of the thus polished semiconductor wafer, wherein the cleaning process follows the CMP process, the method including the step of:
spraying the polished semiconductor wafer with pure water having a predetermined temperature, wherein the predetermined temperature is capable of decreasing a rate of chemical reaction occurring in corrosion of the metallic wiring of the polished semiconductor wafer, wherein the corrosion is caused by an oxidizing agent contained in an abrasive, and the abrasive is used in the CMP process.
In the foregoing second and third aspects, a preferable mode is one wherein the metallic wiring is constructed of a damascene wiring or of a connecting plug.
Further, a preferable mode is one wherein the metallic wiring of the polished semiconductor wafer is formed of metal selected from a group consisting of: copper; aluminum; alloys of copper; alloys of aluminum; or, copper-aluminum alloys.
Still further, a preferable mode is one wherein the predetermined temperature of the pure water is within a range of from 0xc2x0 C. to 25xc2x0 C.
Most preferable mode is one wherein the predetermined temperature of the pure water is within a range of from 0xc2x0 C. to 10xc2x0 C.
Also, according to a fourth aspect of the present invention, there is provided a method for storing a polished semiconductor wafer after completion of its CMP process for a period of time intervened between: the CMP process for forming a metallic wiring in the polished semiconductor wafer; and, a cleaning process of the thus polished semiconductor wafer, wherein the cleaning process follows the CMP process, the method including the step of:
keeping the polished semiconductor wafer immersed in reducing water.
In the foregoing fourth aspect, a preferable mode is one wherein the reducing water is prepared by bubbling hydrogen gas through pure water, or retrieved from a cathode side of pure water during the electrolysis of the pure water.
Also, according to a fifth aspect of the present invention, there is provided an apparatus for storing a polished semiconductor wafer after completion of its CMP process for a period of time intervened between: the CMP process for forming a metallic wiring in the polished semiconductor wafer; and, a cleaning process of the thus polished semiconductor wafer, wherein the cleaning process follows the CMP process, the apparatus including:
a water tank for keeping the polished semiconductor wafer immersed in reducing water.
In the foregoing fifth aspect, a preferable mode is one wherein the water tank is hermetically sealed in a manner such that the water tank has no communication with the atmosphere.
Also, according to a sixth aspect of the present invention, there is provided an apparatus for storing a polished semiconductor wafer after completion of its CMP process for a period of time intervened between: the CMP process for forming a metallic wiring in the polished semiconductor wafer; and, a cleaning process of the thus polished semiconductor wafer, wherein the cleaning process follows the CMP process, the apparatus including:
a water tank for storing said polished semiconductor wafer therein;
a pure water supply means for supplying pure water to the water tank, wherein an anticorrosion agent is added to the pure water to prevents an oxidizing agent contained in an abrasive from chemically attacking the metallic wiring of the polished semiconductor wafer, wherein the abrasive is used in the CMP process;
a recycling means for recycling the pure water together with the anticorrosion agent through both a filter and the water tank; and
a discharging means for discharging out of the water tank the pure water together with the anticorrosion agent both received in the water tank.
In the foregoing aspect, a preferable mode is one wherein the recycling means is provided with a pump and the filter both disposed outside the water tank.
Also, according to a seventh aspect of the present invention, there is provided an apparatus for storing a polished semiconductor wafer after completion of its CMP process for a period of time intervened between: the CMP process for forming a metallic wiring in the polished semiconductor wafer; and, a cleaning process of the thus polished semiconductor wafer, wherein the cleaning process follows the CMP process, the apparatus including:
a water tank for storing the polished semiconductor wafer therein;
a pure water supply means for supplying pure water to the water tank, wherein the pure water having a predetermined temperature which is capable of decreasing a rate of chemical reaction occurring in corrosion of the metallic wiring of the polished semiconductor wafer, wherein the corrosion is caused by an oxidizing agent contained in an abrasive used in the CMP process; and
a discharging means for discharging out of the water tank the pure water together with the anticorrosion agent both received in the water tank.
Furthermore, according to a eighth aspect of the present invention, there is provided an apparatus for storing a polished semiconductor wafer after completion of its CMP process for a period of time intervened between: the CMP process for forming a metallic wiring in the polished semiconductor wafer; and, a cleaning process of the thus polished semiconductor wafer, wherein the cleaning process follows the CMP process, the apparatus including:
a spray means for spraying the polished semiconductor wafer with pure water having a predetermined temperature which is capable of decreasing a rate of chemical reaction occurring in corrosion of the metallic wiring of the polished semiconductor wafer, wherein the corrosion is caused by an oxidizing agent contained in an abrasive used in the CMP process.
In the foregoing eighth aspect, a preferable mode is one wherein the metallic wiring of the polished semiconductor wafer is constructed of a damascene wiring or of a connecting plug.
Further, a preferable mode is one where the predetermined temperature of the pure water is within a range of from 0xc2x0 C. to 25xc2x0 C.
Still further, a most preferable mode is one wherein the predetermined temperature of the pure water is within a range of from 0xc2x0 C. to 10xc2x0 C.
With the above construction, since the anticorrosion agent is capable of adhering to the surface of the polished semiconductor wafer to protect its surface against corrosion, it is possible for the method of the present invention to prevent the exposed surface of the metallic wiring of the polished semiconductor wafer from being chemically attacked in a period of time intervened between the CMP process and the post-CMP cleaning process of the thus polished semiconductor wafer, wherein the post-CMP cleaning process follows the CMP process. Further, by recycling the pure water which is received in the wafer storing water tank and to which pure water the anticorrosion agent has been added, it is also possible for the apparatus and method of the present invention to reduce the amount of the anticorrosion agent used in operation.
Further, in the method of the present invention using the pure water having the above-mentioned predetermined low temperature or supplying the reducing water, since the chemical reaction occurring in corrosion of the Cu or metallic wiring of the polished semiconductor wafer caused by the oxidizing agent derived from the abrasive grain or powder is reduced in reaction rate, it is possible to protect the exposed surface of the metallic wiring of the polished semiconductor wafer 20 against corrosion.
Consequently, in the method and apparatus of the present invention, it is possible to ensure the metallic wiring of the polished semiconductor wafer in its electrical conductivity, and therefore in its reliability in operation. Further, in the method and apparatus of the present invention, since the metallic wiring of the polished semiconductor wafer is free from any corrosion, there is no danger that the metallic wiring is reduced in thickness to produce a shoulder portion in the surface of the polished semiconductor wafer. Consequently, in the method and apparatus of the present invention, there is no danger that the post-CMP cleaning operation of the polished semiconductor wafer becomes poor in cleaning efficiency.